I was on bluesky about to comment on some art someone made and was going to comment it is a diamond in the rough but I did a search to make sure it was rough and not ruff because it is not an expression I use much. When I searched it I found out it meant. "a person who is generally of good character but lacks manners, education, or style; a rough diamond." I just thought it meant hidden gem. Has anyone else misunderstood the meaning of an expression?
Deal with this all the time. I never trust an archaic term because of how many common archaic terms are like that, or worse, with their implications. And idioms like you are citing are really common. A favorite of mine is counting how many famous idioms are just considered excuses to go to the restroom in the Midwest. See a man about a dog? Poo. Take a constitutional? Poo.
Almost all idioms we use commonly actually originally meant the opposite. "Blood is thicker than water" is a longer saying about chosen family being the true strongest bond. "Great minds think alike" finishes with but fools seldom differ. A few bad apples, spoil the bunch. "Pull yourself up by your bootstraps" only a fool would try it. It's the most human thing in the world to twist sayings to mean the opposite.